Ra Gamma Ray constant -Reply

[FRAMEP@ORAU.GOV]

Ted de Castro wrote:

>We need to refine some calculations for our NBS calibrated Ra 226
>source. The NBS certificate declares it equivalent to 901.8
>milligrams of Ra in a0.27mm tube of Thuringian glass.

>What did NBS consider the gamma factor for that source to be in
>1947??

Although this question was more or less directed to NIST folk (Les
etc) I couldn't resist a comment.

The NIST employee you need to speak with is Ron Colle, one of NIST's
more colorful individuals. My impression is that Ron knows more about
radium standardization (not just at NIST) than anyone else you will
find anywhere. He's away from NIST at present and won't be back for a
few weeks. A problem: even when he's in, he never answers the phone -
but he does let you leave a message on his answering machine. If you
sound interesting, he'll return the call. I'll send you his number.

If NIST produced the source, my guess is that they quantified it via
its radon emanation. This would have been measured with pulse
ionization chambers built there in 1943. Obviously this could not be
done after the source was sealed. In the 1950s they usually
quantified sealed radium sources with a 4 pi ion chamber but I don't
think they had one of these in the 1940s. Probably used an ion
chamber though (electroscope/electrometer?).

In any event, they would compare the instrument response to that from
a primary radium standard. They wouldn't worry about a gamma
constants or gamma yeilds for radium. This assumes, perhaps
incorrectly, that you are interested in the sources quantification.
If you are interested in the exposure rate, I have been, regretably,
of zero help. 

Les, any corrections, additions?

Good luck

Paul Frame